1. Field of the Invention
The present invention relates to a valve structure for a hydraulic circuit.
2. Description of the Related Art
In hydraulic circuits, spools are used in regulating flow of hydraulic fluid from an inlet port to an outlet port. A spool is received in a bore having a cylindrical inner wall. The spool has spaced lands. With the lands opposed to the cylindrical inner wall, the spool can move in a longitudinal direction of the bore. The cylindrical inner wall is divided into a plurality of wall segments by a plurality grooves. The grooves are recessed from the cylindrical inner wall. The adjacent two of the grooves, namely an inflow groove and an outflow groove, are separated by a first one of the plurality of wall segments. Inlet and outlet ports are open at the bottoms of the inflow and outflow grooves, respectively. Among the lands, there are two lands, namely an upstream land and a downstream land. The upstream land cooperates with the one wall segment that is disposed between the inflow and outflow grooves. The downstream land cooperates with another wall segment that is spaced from the one wall segment by the outflow groove. Over the stroke of the spool, the downstream land keeps in engagement with the another wall segment and leaves the outflow groove uncovered. Under this condition, a chamber defined in the bore between the two lands is kept in flow communication with the outlet port. At one limit position of the stroke of the piston, the upstream land engages with one wall segment thereby closing flow communication between the inflow groove and the chamber. As the spool moves from this one limit position toward the opposite limit position of the stroke, there is a predetermined position where the upstream land is about to disengage from the one wall segment. When the spool moves further beyond the predetermined position, an inner axial edge of the upstream land leaves the one wall segment thereby defining a gap between them. This gap increases in width as the spool moves further beyond the predetermined position. Hydraulic fluid from the inflow groove flows through this gap toward the outflow groove.
An object of the present invention is to provide an alternative to the valve of the kind mentioned above.